The radius of a soap bubble is reduced rom 5 cm to 1 cm . Then the change in surface energy of the bubble is

Options

A. `1xx10^(-3)`J
B. `1.2 xx 10^(-3)`J
C. ` 2.4 xx 10^(-3)`J
D. `2.8 xx 10^(-3)`J

Answer

B

Explanation

`Delta E = 2Delta AT`
` = 2 xx 4pi(R^(2)-r^(2))T`
` = 2xx 4xx3.1 [(5xx10^(-2))^(2)-(10^(-2))^(2)] xx 2 xx10^(-2)`
` = 8xx3.1 xx 24 xx10^(4)xx2 xx10^(-2)`
` = 1.2 xx10^(-3)`J